The treatment for fin rot and tail is the same. Basically you keep up with daily water changes to try and prevent rot or infection from setting in. AQ salt 1 tsp/gal can also be used, it all depends on how aggressively you treat him.

And from looking at his tail, I see the same feathery bits that my own boy is displaying, it's so frustrating to have a biter. Trying to find out what causes him to bite will help. If it's stress, then turn off the lights and try to keep him calm. If it's boredom, let him have some time flaring at a mirror. Rearrange the decorations in his tank when you change his water. It can be trial and error to figure it out. And the third option is, they're like human nail biters, won't stop, just have bad habits, all we can do is do our best to prevent infection.

thank you so much! that was extremely helpful. i'll keep up with the salt treatment, for how many days would you suggest? coincidentally enough, when i did his water change to add salt about an hour ago, i accidentally ended up rearranging his decorations lol. usually during the day he seems pretty bored, just kind of resting on the leaves, so i hope this helps. i put the other betta tanks that i have on the same desk a teensy bit closer to him, and he's flared a couple times at them so i'll see if that'll keep him amused..i'll move them away in a little while though cuz too much flaring will stress them out, right? i incorrectly thought that bettas NEEDED lots and lots of light so i had a lamp right next to him plus the room's regular light on too, oops. i turned the lamp off now though. im really hoping this isnt a habit..i've had him for more than 6 months and only today has his tail looked any different, so im hoping its a passing thing.
however, the orange guy (the reason i started this thread) has a very different tail situation. i can't take a picture but its jagged, has black outlining and is different than it was yesterday. i think this guy does have fin rot so i put him in salt treatment too.

The actual treatment for both is the same, daily water changes, with similar temperature water. 1tsp/ AQ salt (not to be confused with table salt) can be used to treat, for no more than 10 days.
You might try to pick up some new food, either frozen, or live foods like brine shrimp, blood worms, or live "feeder" fry and mosquito larvae (ew, but they like it). Small meals fed throughout the day can help with the fin regrowth. It can be kinda gross when you're feeding frozen blood worms (and the smell isn't too fresh either), but a high protein diet can help. IF you can't do this, then a high protein meal, one that doesn't have wheat or other such ingredients as it's first three ingredients. 42% is on the lower end of the range, which is what I feed my boy, Omega one. First three ingredients are fish.
API stress coat can sometimes help, I've used it on my boy after a bad fin chewing episode. OFL and others have also recommended tannins, like dried IAL leaf, or oak leaf, or, if failing that, even decaf (absolutely plain as can be, nothing added, no caffeine in sight!) green tea. This darkens the water, which helps calm them, and it provides other benefits to help them recover.

The actual treatment for both is the same, daily water changes, with similar temperature water. 1tsp/ AQ salt (not to be confused with table salt) can be used to treat, for no more than 10 days.
You might try to pick up some new food, either frozen, or live foods like brine shrimp, blood worms, or live "feeder" fry and mosquito larvae (ew, but they like it). Small meals fed throughout the day can help with the fin regrowth. It can be kinda gross when you're feeding frozen blood worms (and the smell isn't too fresh either), but a high protein diet can help. IF you can't do this, then a high protein meal, one that doesn't have wheat or other such ingredients as it's first three ingredients. 42% is on the lower end of the range, which is what I feed my boy, Omega one. First three ingredients are fish.
API stress coat can sometimes help, I've used it on my boy after a bad fin chewing episode. OFL and others have also recommended tannins, like dried IAL leaf, or oak leaf, or, if failing that, even decaf (absolutely plain as can be, nothing added, no caffeine in sight!) green tea. This darkens the water, which helps calm them, and it provides other benefits to help them recover.

yea i feed them pellets every day and bloodworms twice a week or so. api stress coat is what ive been using to condition the water for every water change on all my 6 bettas since i got my first one, its fantastic :) i'll look into the tannins, i definitely want these guys to get better ASAP. im leaving on a trip in a few weeks so my mom is going to have to be caring for them, and i dont want to put her through the trouble of having to care for sick fish, so i hope they get better soon

Yea, mothers will do one of two things, decide they know best and feed how much they want, or they will follow your instructions exactly. Left my boy with my mother while I'm away from the summer. She's done wonderfully *knocks wood*. Hope your mom will be as good with yours.

Yea, mothers will do one of two things, decide they know best and feed how much they want, or they will follow your instructions exactly. Left my boy with my mother while I'm away from the summer. She's done wonderfully *knocks wood*. Hope your mom will be as good with yours.